Selection for carcass length in Large White pigs

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Abstract
A sib selection programme for length of carcass was carried out for five generations within a closed herd of Large White pigs. A generation interval of one year was obtained. Litter production was good throughout the project and the numbers of pigs born and reared in the final generation were 11·2 and 10·3 respectively. Overall response to selection was predicted with reasonable success. The increase in length was associated with an increase in number of vertebrae. Heritability for length of carcass computed from the pooled components of variance was 0·53 ± 0·12. Realized heritability was 0·5 ± 0·1. No control strain was maintained. Correlated traits moved in the expected directions and responses were beneficial for traits such as backfat measurements and chest depth, but unfavourable for belly thickness and ham conformation. Carcass acceptability was not good initially and this deteriorated during the project. The difficulties involved in maintaining selection pressure and herd size are discussed. Abnormalities and lameness were recorded and did not increase systematically over the experiment. It is suggested that the specific relationships between ‘conformation’, carcass value and viability require further investigation with particular reference to length of leg and length of carcass.